The invention concerns a method of controlling an occupant-head protection system with one or more active head protection elements in a vehicle, in which the respective active head protection element is triggered when predeterminable triggering conditions indicative of a vehicle collision exist, comprising the exceeding of a predeterminable collision threshold value by a characteristic variable indicative of a collision. An active head protection element is to be understood here as meaning a protection element for the head of a vehicle occupant which is intended to prevent the known problem of the occurrence of a cervical vertebra whiplash syndrome in the case of a collision. Such protection elements may be in particular so-called active headrests in the form of pivotable headrests or head airbags, but also other suitable safety devices for avoiding the cervical vertebra whiplash syndrome, such as for example an actively downward-pivotable seat backrest. These protection elements can be actively controlled from an initial state into a different, occupant-head-protecting state when the triggering conditions concerned exist.
DE 196 47 660 A1 discloses a triggering device for active occupant restraining systems, such as belt pretensioners or airbags, in a motor vehicle. This triggering device is assigned an acceleration sensor, which in the event of a vehicle collision provides a deceleration signal. The triggering of at least one of the restraining systems takes place when a triggering threshold of the deceleration signal is exceeded. The triggering device is further connected to an object-sensing unit, with which obstacles within close range of the vehicle are sensed and the associated relative speed is determined. The triggering threshold is varied in dependence on the speed of the vehicle itself and the relative speed of sensed obstacles. In particular when no obstacle is sensed, the triggering threshold is raised as the speed of the vehicle itself falls.
DE 43 34 671 A1 discloses a restraining system with a restraining device and a central control unit. In the control unit, a central acceleration sensor and wheel-speed sensors of an antilock braking system (ABS) are assessed to decide on the triggering of the restraining device. Even in the case of initially small vehicle decelerations, the control unit initiates a triggering of the restraining device in the event that a relatively great wheel deceleration of at least one front wheel is established by means of the wheel-speed sensors. This is intended to achieve the effect that a triggering decision is reached in time in the control unit even in the case of problem crashes, for example soft collisions.
DE 37 37 554 A1 also gives a description of a triggering system for active occupant protection devices, such as belt pretensioners and airbags, in which, for increasing the system reliability, information from an ABS, such as for example wheel speed information, is also assessed.
DE 39 42 011 A1 discloses a device for triggering safety devices for occupants of a motor vehicle, such as airbags or belt pretensioners, in which an output signal of an acceleration sensor is assessed in an evaluation circuit to ascertain whether impact not relevant to triggering, in particular a "hammer blow", on the vehicle or an acceleration of the vehicle relevant to triggering exists. Furthermore, the evaluation circuit comprises a rear-collision detection circuit, it being intended that the safety devices are not triggered in the case of a detected rear collision.
DE 43 35 991 A1 discloses a device for triggering restraining means in a motor vehicle in which, along with acceleration-sensor signals, vehicle-dynamic movement and/or status data, such as speed, brake actuation, brake pressure etc., are assessed. These signals are fed to a central control unit, for example via a data bus, and influence a triggering algorithm in such a way that in the case of high vehicle speeds fast triggering of the restraining means takes place and in the case of steering maneuvers the direction of the collision to be expected is predetermined in particular.
In DE 88 16 763 U1 there is a description of a device for triggering restraining means, which has an acceleration pickup, the signals of which are evaluated in a control unit and, if appropriate, lead to the triggering of one or more restraining means. The control unit comprises means for establishing the direction of the acceleration acting on the vehicle and consequently for distinguishing between different types of collision. Depending on the established direction of the collision, selectively suitable restraining means are triggered and the others are kept deactivated. In particular, triggering of the restraining means provided there does not take place in the event of a rear collision.
EP 0 593 845 A1 discloses a head airbag with a triggering device, which is accommodated in the headrest of a seat. The triggering of the head airbag takes place on the basis of the signal of an impact sensor which is arranged at or in the vicinity of the rear of the vehicle and is thus able to detect impact acting on the rear region as the result of a collision.
In U.S. Pat. No. 5,605,202 there is described an occupant restraining system in a vehicle, in which accident sensors, such as for example acceleration pickups, acceleration dynamometers, inertia sensors or the like, are constantly monitored and interrogated by means of a control device. This serves on the one hand for functional testing and on the other hand, if appropriate, for initiating the triggering of the restraining means. Since continuous monitoring of the faultless functioning of the accident sensors is time-intensive and adversely affects the response time of the occupant restraining system, the control unit evaluates not only signals from accident sensors but also data from additional sensors concerning the state of movement of the vehicle, such as for example wheel-speed or brake-pressure sensors. If these data indicate a situation where there is a risk of an accident, the functional monitoring of the accident sensors is suspended and an alarm status is established for the occupant restraining systems, in which the latter can trigger without delay.
In the conference publication "Airbag 2000", 3rd Int. Symp. on Sophisticated Car Occupant Safety Systems, Karlsruhe, Germany, Nov. 26 and 27, 1996, it is proposed under the title "Smart Restraint Management--An Innovative and Comprehensive Concept" by L. Grosch et al. to provide for an occupant restraining system in the front region of a vehicle a sensor which measures the approach speed of a collision obstacle. With this signal, the triggering threshold of a central accident sensor can be influenced to achieve earlier triggering of occupant restraining systems.
Under the title "Pre-Crash Sensors", in the same conference publication, H. Spies presents the concept of feeding to a central control unit for occupant restraining systems signals from obstacle approach sensors which are provided in the front region and the rear of a vehicle, signals from vehicle-dynamics sensors and vehicle data from an ABS system, but also data which concern the status of the door locking, etc. These data are evaluated in the central control unit, whereupon the occupant restraining systems are activated in such a way that they are fired step by step in a way corresponding to the accident situation and in this case the filling pressure in airbags can be adapted to requirements.